In recent years, in a wireless communication system such as a mobile phone system, discussion is being conducted on the next generation wireless communication technology in order to further increase the speed and increase the capacity, etc. of wireless communication. For example, in a communication standard called LTE (Long Term Evolution), a technique of performing communication using a carrier wave in a frequency band that requires a license (LC: Licensed band Carrier) and a carrier wave in a frequency band that does not require a license (UC: Unlicensed band Carrier) is being studied. The technique is called LAA (Licensed Assisted Access).
In LAA, when a terminal performs UL (Up Link) transmission to a base station in the unlicensed band, the base station transmits a UL grant for requiring data transmission to the terminal via a licensed band. The base station then executes LBT (Listen Before Talk) in the unlicensed band, for example, before the terminal performs transmission in UL. When the unlicensed band is detected idle, the base station examines whether to transmit a reservation signal to the unlicensed band until a transmission timing of the terminal, for example, in order that the terminal ensures the unlicensed band used for UL data transmission. Thus, the terminal can perform UL data transmission using the unlicensed band after a predetermined period of time from the UL grant.
Non Patent Literature 1: 3GPP RANI Contribution R1-50186
Incidentally, in the technique of the non patent literature, when a busy state of the unlicensed band continues and the terminal does not receive the reservation signal in the unlicensed band by the time of timing of the UL data transmission, the terminal cancels, for example, the UL data transmission. As a result, the transmission opportunity of data scheduled to be transmitted by the terminal is postponed until a predetermined period of time passes since the next UL grant transmitted from the terminal. Therefore, the throughput of data transmission in UL from the terminal to the base station may decrease.